This invention relates to a single compact dental material formed from laminated multiple metallic layers with at least two of the layers composed of different metal compositions in an alternating arrangement for use in forming a dental crown or bridge or for repairing a dental restoration and to a method of forming a dental coping from a single compact dental material in a single heat treatment.
A metal coping is used in dentistry in the construction of a dental crown and/or bridge. The metal coping functions as the under structure of the crown and is usually covered, for reasons of aesthetics, with a fired-on coating of a ceramic porcelain composition or a polymer based veneering material. The metal coping supports the coating and provides the required structural strength and rigidity for the restored tooth to resist the forces of mastication.
A metal coping may be cast from an investment of a wax or plastic pattern of the tooth to be restored. An alternative procedure which does not require waxing, investing or casting and which currently has been gaining wide acceptance by many laboratory practitioners and dentists is to form the coping from a moldable dental material composition composed of a mixture of high and low fusing temperature metal particles, as disclosed, for example, in U.S. Pat. Nos. 5,234,343 and 5,332,622 respectively. The dental material as taught in these patents, the disclosure of which is herein incorporated by reference, forms a porous structure upon heat treatment having a high void volume of above at least 20%. Before heat treatment the dental material is molded into the shape of the tooth to be restored. The molded shape is self-supported and is converted upon heat treatment in a dental furnace into a porous structure essentially any without shrinkage. The heat treatment temperature must be sufficient to entirely or substantially melt the low fusing temperature metal particles but not the high fusing temperature metal particles. This results in the low fusing temperature metal particles interconnecting the high fusing temperature metal particles to form the porous structure without affecting the shape of the structure. The porous structure has a high void volume which is then filled to solidify the structure by adding a filler material of a metal or ceramic in a secondary heat treatment procedure.
In U.S. Pat. No. 5,593,305, the disclosure of which is herein incorporated by reference, it is further taught that the moldable dental material may be formed into a compacted strip formed of a base material of the high and low fusing temperature metal particles and wax. Likewise the filler material may also be in a compacted strip of the filler composition and wax. The strip of base material is hand molded over the surface of a die and heat treated followed by a similar procedure for the strip of filler material in a secondary heat treatment operation.
A dental material has been discovered in accordance with the present invention comprising a laminated structure of at least three layers with at least one of the layers composed of a base material composition containing high fusing temperature metal particles and with at least another layer comprising a filler material composition of low fusing temperature metal particles with said layers arranged adjacent to one another in an alternating sequence for forming a dental coping or for repairing a dental restoration upon firing the structure in a dental furnace at a temperature at least equal to the melting temperature of the low fusing temperature metal particles but below the melting temperature of the high fusing temperature metal particles. The dental material of the present invention is adapted to solidify upon heat treatment with the layers of filler material merging into the layers of the base material. The alternating arrangement of layers, the composition of the layers and the thickness of the layers control the degree of diffusion of the filler material into the layer(s) of base material. The diffusion occurs substantially simultaneous with the conversion of the base layer(s) into a porous structure. The layer(s) of filler material merge into the porous structure formed by the base material during heat treatment and solidify into a dental coping. The physical properties of the dental coping following heat treatment such as e.g., its hardness can be modified by variation of the composition and/or thickness of the layers. The arrangement of layers and their composition may also be varied to improve the adaptability of the surface layer to a fired-on coating of porcelain and/or to improve its adaptability to cementation.
It has been further discovered in accordance with the present invention that the laminated structure can be heat treated in a dental furnace in one firing, i.e., only one firing sequence, with the heat treatment carried out in stages either manually or automatically. Heretofore, it was essential for the base material composition to be physically separated from the filler material composition and for heat treatment to be carried out in at least two separate and distinct firing operations. Stated otherwise, heretofore it was essential to form a porous structure from the base material composition in one heat treatment operation before filler material could be added in a separate heat treatment operation to densify the porous structure.
The method of the present invention for forming a dental coping comprises the steps of: forming at least one sheet of a base material composition containing high fusing temperature metal particles and a wax binder; forming at least a second sheet of a filler material composition of low fusing temperature metal particles and a wax binder, laminating the sheet(s) of base material with the sheet(s) of filler material in an alternating sequence to form at least three laminated layers in which each sheet of base material lies adjacent to a sheet of filler material and selecting a thickness and binder concentration for each layer such that the layer(s) of filler material will impregnate the layer(s) of base material in one heat treatment operation and cause the layers of base material to converge.